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  <title>JavaScript 算数</title>
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<h2>算数运算符</h2>
<p>典型的算术运算会操作两个数（或表达式）并返回一个新的数。</p>

<p id="demo"></p>

<script>
  var x = 7 + 8;
  document.getElementById("demo").innerHTML = x;
</script>


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